Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | :mod:`subprocess` --- Subprocess management |
| 2 | =========================================== |
| 3 | |
| 4 | .. module:: subprocess |
| 5 | :synopsis: Subprocess management. |
| 6 | .. moduleauthor:: Peter Åstrand <astrand@lysator.liu.se> |
| 7 | .. sectionauthor:: Peter Åstrand <astrand@lysator.liu.se> |
| 8 | |
| 9 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 10 | The :mod:`subprocess` module allows you to spawn new processes, connect to their |
| 11 | input/output/error pipes, and obtain their return codes. This module intends to |
| 12 | replace several other, older modules and functions, such as:: |
| 13 | |
| 14 | os.system |
| 15 | os.spawn* |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 16 | |
| 17 | Information about how the :mod:`subprocess` module can be used to replace these |
| 18 | modules and functions can be found in the following sections. |
| 19 | |
Benjamin Peterson | 4118174 | 2008-07-02 20:22:54 +0000 | [diff] [blame] | 20 | .. seealso:: |
| 21 | |
| 22 | :pep:`324` -- PEP proposing the subprocess module |
| 23 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 24 | |
| 25 | Using the subprocess Module |
| 26 | --------------------------- |
| 27 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 28 | The recommended approach to invoking subprocesses is to use the following |
| 29 | convenience functions for all use cases they can handle. For more advanced |
| 30 | use cases, the underlying :class:`Popen` interface can be used directly. |
| 31 | |
| 32 | |
| 33 | .. function:: call(args, *, stdin=None, stdout=None, stderr=None, shell=False) |
| 34 | |
| 35 | Run the command described by *args*. Wait for command to complete, then |
| 36 | return the :attr:`returncode` attribute. |
| 37 | |
| 38 | The arguments shown above are merely the most common ones, described below |
| 39 | in :ref:`frequently-used-arguments` (hence the slightly odd notation in |
| 40 | the abbreviated signature). The full function signature is the same as |
| 41 | that of the :class:`Popen` constructor - this functions passes all |
| 42 | supplied arguments directly through to that interface. |
| 43 | |
| 44 | Examples:: |
| 45 | |
| 46 | >>> subprocess.call(["ls", "-l"]) |
| 47 | 0 |
| 48 | |
| 49 | >>> subprocess.call("exit 1", shell=True) |
| 50 | 1 |
| 51 | |
| 52 | .. warning:: |
| 53 | |
| 54 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 55 | if combined with untrusted input. See the warning under |
| 56 | :ref:`frequently-used-arguments` for details. |
| 57 | |
| 58 | .. note:: |
| 59 | |
| 60 | Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As |
| 61 | the pipes are not being read in the current process, the child |
| 62 | process may block if it generates enough output to a pipe to fill up |
| 63 | the OS pipe buffer. |
| 64 | |
| 65 | |
| 66 | .. function:: check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False) |
| 67 | |
| 68 | Run command with arguments. Wait for command to complete. If the return |
| 69 | code was zero then return, otherwise raise :exc:`CalledProcessError`. The |
| 70 | :exc:`CalledProcessError` object will have the return code in the |
| 71 | :attr:`returncode` attribute. |
| 72 | |
| 73 | The arguments shown above are merely the most common ones, described below |
| 74 | in :ref:`frequently-used-arguments` (hence the slightly odd notation in |
| 75 | the abbreviated signature). The full function signature is the same as |
| 76 | that of the :class:`Popen` constructor - this functions passes all |
| 77 | supplied arguments directly through to that interface. |
| 78 | |
| 79 | Examples:: |
| 80 | |
| 81 | >>> subprocess.check_call(["ls", "-l"]) |
| 82 | 0 |
| 83 | |
| 84 | >>> subprocess.check_call("exit 1", shell=True) |
| 85 | Traceback (most recent call last): |
| 86 | ... |
| 87 | subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 |
| 88 | |
| 89 | .. versionadded:: 2.5 |
| 90 | |
| 91 | .. warning:: |
| 92 | |
| 93 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 94 | if combined with untrusted input. See the warning under |
| 95 | :ref:`frequently-used-arguments` for details. |
| 96 | |
| 97 | .. note:: |
| 98 | |
| 99 | Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As |
| 100 | the pipes are not being read in the current process, the child |
| 101 | process may block if it generates enough output to a pipe to fill up |
| 102 | the OS pipe buffer. |
| 103 | |
| 104 | |
| 105 | .. function:: check_output(args, *, stdin=None, stderr=None, shell=False, universal_newlines=False) |
| 106 | |
| 107 | Run command with arguments and return its output as a byte string. |
| 108 | |
| 109 | If the return code was non-zero it raises a :exc:`CalledProcessError`. The |
| 110 | :exc:`CalledProcessError` object will have the return code in the |
| 111 | :attr:`returncode` attribute and any output in the :attr:`output` |
| 112 | attribute. |
| 113 | |
| 114 | The arguments shown above are merely the most common ones, described below |
| 115 | in :ref:`frequently-used-arguments` (hence the slightly odd notation in |
| 116 | the abbreviated signature). The full function signature is largely the |
| 117 | same as that of the :class:`Popen` constructor, except that *stdout* is |
| 118 | not permitted as it is used internally. All other supplied arguments are |
| 119 | passed directly through to the :class:`Popen` constructor. |
| 120 | |
| 121 | Examples:: |
| 122 | |
| 123 | >>> subprocess.check_output(["echo", "Hello World!"]) |
| 124 | b'Hello World!\n' |
| 125 | |
| 126 | >>> subprocess.check_output(["echo", "Hello World!"], universal_newlines=True) |
| 127 | 'Hello World!\n' |
| 128 | |
| 129 | >>> subprocess.check_output("exit 1", shell=True) |
| 130 | Traceback (most recent call last): |
| 131 | ... |
| 132 | subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 |
| 133 | |
| 134 | By default, this function will return the data as encoded bytes. The actual |
| 135 | encoding of the output data may depend on the command being invoked, so the |
| 136 | decoding to text will often need to be handled at the application level. |
| 137 | |
| 138 | This behaviour may be overridden by setting *universal_newlines* to |
| 139 | :const:`True` as described below in :ref:`frequently-used-arguments`. |
| 140 | |
| 141 | To also capture standard error in the result, use |
| 142 | ``stderr=subprocess.STDOUT``:: |
| 143 | |
| 144 | >>> subprocess.check_output( |
| 145 | ... "ls non_existent_file; exit 0", |
| 146 | ... stderr=subprocess.STDOUT, |
| 147 | ... shell=True) |
| 148 | 'ls: non_existent_file: No such file or directory\n' |
| 149 | |
| 150 | .. versionadded:: 2.7 |
| 151 | |
| 152 | .. warning:: |
| 153 | |
| 154 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 155 | if combined with untrusted input. See the warning under |
| 156 | :ref:`frequently-used-arguments` for details. |
| 157 | |
| 158 | .. note:: |
| 159 | |
| 160 | Do not use ``stderr=PIPE`` with this function. As the pipe is not being |
| 161 | read in the current process, the child process may block if it |
| 162 | generates enough output to the pipe to fill up the OS pipe buffer. |
| 163 | |
| 164 | |
| 165 | .. data:: PIPE |
| 166 | |
| 167 | Special value that can be used as the *stdin*, *stdout* or *stderr* argument |
| 168 | to :class:`Popen` and indicates that a pipe to the standard stream should be |
| 169 | opened. |
| 170 | |
| 171 | |
| 172 | .. data:: STDOUT |
| 173 | |
| 174 | Special value that can be used as the *stderr* argument to :class:`Popen` and |
| 175 | indicates that standard error should go into the same handle as standard |
| 176 | output. |
| 177 | |
| 178 | |
| 179 | .. _frequently-used-arguments: |
| 180 | |
| 181 | Frequently Used Arguments |
| 182 | ^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 183 | |
| 184 | To support a wide variety of use cases, the :class:`Popen` constructor (and |
| 185 | the convenience functions) accept a large number of optional arguments. For |
| 186 | most typical use cases, many of these arguments can be safely left at their |
| 187 | default values. The arguments that are most commonly needed are: |
| 188 | |
| 189 | *args* is required for all calls and should be a string, or a sequence of |
| 190 | program arguments. Providing a sequence of arguments is generally |
| 191 | preferred, as it allows the module to take care of any required escaping |
| 192 | and quoting of arguments (e.g. to permit spaces in file names). If passing |
| 193 | a single string, either *shell* must be :const:`True` (see below) or else |
| 194 | the string must simply name the program to be executed without specifying |
| 195 | any arguments. |
| 196 | |
| 197 | *stdin*, *stdout* and *stderr* specify the executed program's standard input, |
| 198 | standard output and standard error file handles, respectively. Valid values |
| 199 | are :data:`PIPE`, an existing file descriptor (a positive integer), an |
| 200 | existing file object, and ``None``. :data:`PIPE` indicates that a new pipe |
| 201 | to the child should be created. With the default settings of ``None``, no |
| 202 | redirection will occur; the child's file handles will be inherited from the |
| 203 | parent. Additionally, *stderr* can be :data:`STDOUT`, which indicates that |
| 204 | the stderr data from the child process should be captured into the same file |
| 205 | handle as for stdout. |
| 206 | |
| 207 | When *stdout* or *stderr* are pipes and *universal_newlines* is |
| 208 | :const:`True` then the output data is assumed to be encoded as UTF-8 and |
| 209 | will automatically be decoded to text. All line endings will be converted |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 210 | to ``'\n'`` as described for the universal newlines ``'U'`` mode argument |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 211 | to :func:`open`. |
| 212 | |
| 213 | If *shell* is :const:`True`, the specified command will be executed through |
| 214 | the shell. This can be useful if you are using Python primarily for the |
| 215 | enhanced control flow it offers over most system shells and still want |
| 216 | access to other shell features such as filename wildcards, shell pipes and |
| 217 | environment variable expansion. |
| 218 | |
| 219 | .. warning:: |
| 220 | |
| 221 | Executing shell commands that incorporate unsanitized input from an |
| 222 | untrusted source makes a program vulnerable to `shell injection |
| 223 | <http://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_, |
| 224 | a serious security flaw which can result in arbitrary command execution. |
| 225 | For this reason, the use of *shell=True* is **strongly discouraged** in cases |
| 226 | where the command string is constructed from external input:: |
| 227 | |
| 228 | >>> from subprocess import call |
| 229 | >>> filename = input("What file would you like to display?\n") |
| 230 | What file would you like to display? |
| 231 | non_existent; rm -rf / # |
| 232 | >>> call("cat " + filename, shell=True) # Uh-oh. This will end badly... |
| 233 | |
| 234 | ``shell=False`` disables all shell based features, but does not suffer |
| 235 | from this vulnerability; see the Note in the :class:`Popen` constructor |
| 236 | documentation for helpful hints in getting ``shell=False`` to work. |
| 237 | |
| 238 | These options, along with all of the other options, are described in more |
| 239 | detail in the :class:`Popen` constructor documentation. |
| 240 | |
| 241 | |
Sandro Tosi | 1526ad1 | 2011-12-25 11:27:37 +0100 | [diff] [blame] | 242 | Popen Constructor |
Sandro Tosi | 3e6c814 | 2011-12-25 17:14:11 +0100 | [diff] [blame] | 243 | ^^^^^^^^^^^^^^^^^ |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 244 | |
| 245 | The underlying process creation and management in this module is handled by |
| 246 | the :class:`Popen` class. It offers a lot of flexibility so that developers |
| 247 | are able to handle the less common cases not covered by the convenience |
| 248 | functions. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 249 | |
| 250 | |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 251 | .. class:: Popen(args, bufsize=0, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=True, shell=False, cwd=None, env=None, universal_newlines=False, startupinfo=None, creationflags=0, restore_signals=True, start_new_session=False, pass_fds=()) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 252 | |
| 253 | Arguments are: |
| 254 | |
Benjamin Peterson | d18de0e | 2008-07-31 20:21:46 +0000 | [diff] [blame] | 255 | *args* should be a string, or a sequence of program arguments. The program |
Benjamin Peterson | fa0d703 | 2009-06-01 22:42:33 +0000 | [diff] [blame] | 256 | to execute is normally the first item in the args sequence or the string if |
| 257 | a string is given, but can be explicitly set by using the *executable* |
| 258 | argument. When *executable* is given, the first item in the args sequence |
| 259 | is still treated by most programs as the command name, which can then be |
| 260 | different from the actual executable name. On Unix, it becomes the display |
| 261 | name for the executing program in utilities such as :program:`ps`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 262 | |
| 263 | On Unix, with *shell=False* (default): In this case, the Popen class uses |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 264 | :meth:`os.execvp` like behavior to execute the child program. |
| 265 | *args* should normally be a |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 266 | sequence. If a string is specified for *args*, it will be used as the name |
| 267 | or path of the program to execute; this will only work if the program is |
| 268 | being given no arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 269 | |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 270 | .. note:: |
| 271 | |
| 272 | :meth:`shlex.split` can be useful when determining the correct |
| 273 | tokenization for *args*, especially in complex cases:: |
| 274 | |
| 275 | >>> import shlex, subprocess |
R. David Murray | 73bc75b | 2010-02-05 16:25:12 +0000 | [diff] [blame] | 276 | >>> command_line = input() |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 277 | /bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'" |
| 278 | >>> args = shlex.split(command_line) |
| 279 | >>> print(args) |
| 280 | ['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"] |
| 281 | >>> p = subprocess.Popen(args) # Success! |
| 282 | |
| 283 | Note in particular that options (such as *-input*) and arguments (such |
| 284 | as *eggs.txt*) that are separated by whitespace in the shell go in separate |
| 285 | list elements, while arguments that need quoting or backslash escaping when |
| 286 | used in the shell (such as filenames containing spaces or the *echo* command |
| 287 | shown above) are single list elements. |
| 288 | |
| 289 | On Unix, with *shell=True*: If args is a string, it specifies the command |
| 290 | string to execute through the shell. This means that the string must be |
| 291 | formatted exactly as it would be when typed at the shell prompt. This |
| 292 | includes, for example, quoting or backslash escaping filenames with spaces in |
| 293 | them. If *args* is a sequence, the first item specifies the command string, and |
| 294 | any additional items will be treated as additional arguments to the shell |
| 295 | itself. That is to say, *Popen* does the equivalent of:: |
| 296 | |
| 297 | Popen(['/bin/sh', '-c', args[0], args[1], ...]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 298 | |
R. David Murray | c7399d0 | 2010-11-12 00:35:31 +0000 | [diff] [blame] | 299 | .. warning:: |
| 300 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 301 | Enabling this option can be a security hazard if combined with untrusted |
| 302 | input. See the warning under :ref:`frequently-used-arguments` |
| 303 | for details. |
R. David Murray | c7399d0 | 2010-11-12 00:35:31 +0000 | [diff] [blame] | 304 | |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 305 | On Windows: the :class:`Popen` class uses CreateProcess() to execute the |
| 306 | child program, which operates on strings. If *args* is a sequence, it will |
| 307 | be converted to a string in a manner described in |
| 308 | :ref:`converting-argument-sequence`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 309 | |
| 310 | *bufsize*, if given, has the same meaning as the corresponding argument to the |
| 311 | built-in open() function: :const:`0` means unbuffered, :const:`1` means line |
| 312 | buffered, any other positive value means use a buffer of (approximately) that |
| 313 | size. A negative *bufsize* means to use the system default, which usually means |
| 314 | fully buffered. The default value for *bufsize* is :const:`0` (unbuffered). |
| 315 | |
Antoine Pitrou | 4b87620 | 2010-06-02 17:10:49 +0000 | [diff] [blame] | 316 | .. note:: |
| 317 | |
| 318 | If you experience performance issues, it is recommended that you try to |
| 319 | enable buffering by setting *bufsize* to either -1 or a large enough |
| 320 | positive value (such as 4096). |
| 321 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 322 | The *executable* argument specifies the program to execute. It is very seldom |
| 323 | needed: Usually, the program to execute is defined by the *args* argument. If |
| 324 | ``shell=True``, the *executable* argument specifies which shell to use. On Unix, |
| 325 | the default shell is :file:`/bin/sh`. On Windows, the default shell is |
Alexandre Vassalotti | 260484d | 2009-07-17 11:43:26 +0000 | [diff] [blame] | 326 | specified by the :envvar:`COMSPEC` environment variable. The only reason you |
| 327 | would need to specify ``shell=True`` on Windows is where the command you |
| 328 | wish to execute is actually built in to the shell, eg ``dir``, ``copy``. |
| 329 | You don't need ``shell=True`` to run a batch file, nor to run a console-based |
| 330 | executable. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 331 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 332 | *stdin*, *stdout* and *stderr* specify the executed program's standard input, |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 333 | standard output and standard error file handles, respectively. Valid values |
| 334 | are :data:`PIPE`, an existing file descriptor (a positive integer), an |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 335 | existing :term:`file object`, and ``None``. :data:`PIPE` indicates that a |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 336 | new pipe to the child should be created. With the default settings of |
| 337 | ``None``, no redirection will occur; the child's file handles will be |
| 338 | inherited from the parent. Additionally, *stderr* can be :data:`STDOUT`, |
| 339 | which indicates that the stderr data from the applications should be |
| 340 | captured into the same file handle as for stdout. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 341 | |
| 342 | If *preexec_fn* is set to a callable object, this object will be called in the |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 343 | child process just before the child is executed. |
| 344 | (Unix only) |
| 345 | |
| 346 | .. warning:: |
| 347 | |
| 348 | The *preexec_fn* parameter is not safe to use in the presence of threads |
| 349 | in your application. The child process could deadlock before exec is |
| 350 | called. |
| 351 | If you must use it, keep it trivial! Minimize the number of libraries |
| 352 | you call into. |
| 353 | |
| 354 | .. note:: |
| 355 | |
| 356 | If you need to modify the environment for the child use the *env* |
| 357 | parameter rather than doing it in a *preexec_fn*. |
| 358 | The *start_new_session* parameter can take the place of a previously |
| 359 | common use of *preexec_fn* to call os.setsid() in the child. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 360 | |
| 361 | If *close_fds* is true, all file descriptors except :const:`0`, :const:`1` and |
| 362 | :const:`2` will be closed before the child process is executed. (Unix only). |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 363 | The default varies by platform: Always true on Unix. On Windows it is |
| 364 | true when *stdin*/*stdout*/*stderr* are :const:`None`, false otherwise. |
Gregory P. Smith | d23047b | 2010-12-04 09:10:44 +0000 | [diff] [blame] | 365 | On Windows, if *close_fds* is true then no handles will be inherited by the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 366 | child process. Note that on Windows, you cannot set *close_fds* to true and |
| 367 | also redirect the standard handles by setting *stdin*, *stdout* or *stderr*. |
| 368 | |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 369 | .. versionchanged:: 3.2 |
| 370 | The default for *close_fds* was changed from :const:`False` to |
| 371 | what is described above. |
| 372 | |
| 373 | *pass_fds* is an optional sequence of file descriptors to keep open |
| 374 | between the parent and child. Providing any *pass_fds* forces |
| 375 | *close_fds* to be :const:`True`. (Unix only) |
| 376 | |
| 377 | .. versionadded:: 3.2 |
| 378 | The *pass_fds* parameter was added. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 379 | |
| 380 | If *cwd* is not ``None``, the child's current directory will be changed to *cwd* |
| 381 | before it is executed. Note that this directory is not considered when |
| 382 | searching the executable, so you can't specify the program's path relative to |
| 383 | *cwd*. |
| 384 | |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 385 | If *restore_signals* is True (the default) all signals that Python has set to |
| 386 | SIG_IGN are restored to SIG_DFL in the child process before the exec. |
| 387 | Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. |
| 388 | (Unix only) |
| 389 | |
| 390 | .. versionchanged:: 3.2 |
| 391 | *restore_signals* was added. |
| 392 | |
| 393 | If *start_new_session* is True the setsid() system call will be made in the |
| 394 | child process prior to the execution of the subprocess. (Unix only) |
| 395 | |
| 396 | .. versionchanged:: 3.2 |
| 397 | *start_new_session* was added. |
| 398 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 399 | If *env* is not ``None``, it must be a mapping that defines the environment |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 400 | variables for the new process; these are used instead of the default |
| 401 | behavior of inheriting the current process' environment. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 402 | |
R. David Murray | 1055e89 | 2009-04-16 18:15:32 +0000 | [diff] [blame] | 403 | .. note:: |
R. David Murray | f4ac149 | 2009-04-15 22:35:15 +0000 | [diff] [blame] | 404 | |
Georg Brandl | 2708f3a | 2009-12-20 14:38:23 +0000 | [diff] [blame] | 405 | If specified, *env* must provide any variables required for the program to |
| 406 | execute. On Windows, in order to run a `side-by-side assembly`_ the |
| 407 | specified *env* **must** include a valid :envvar:`SystemRoot`. |
R. David Murray | f4ac149 | 2009-04-15 22:35:15 +0000 | [diff] [blame] | 408 | |
R. David Murray | 1055e89 | 2009-04-16 18:15:32 +0000 | [diff] [blame] | 409 | .. _side-by-side assembly: http://en.wikipedia.org/wiki/Side-by-Side_Assembly |
| 410 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 411 | If *universal_newlines* is :const:`True`, the file objects stdout and stderr are |
| 412 | opened as text files, but lines may be terminated by any of ``'\n'``, the Unix |
Georg Brandl | c575c90 | 2008-09-13 17:46:05 +0000 | [diff] [blame] | 413 | end-of-line convention, ``'\r'``, the old Macintosh convention or ``'\r\n'``, the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 414 | Windows convention. All of these external representations are seen as ``'\n'`` |
| 415 | by the Python program. |
| 416 | |
| 417 | .. note:: |
| 418 | |
Georg Brandl | 7f01a13 | 2009-09-16 15:58:14 +0000 | [diff] [blame] | 419 | This feature is only available if Python is built with universal newline |
| 420 | support (the default). Also, the newlines attribute of the file objects |
| 421 | :attr:`stdout`, :attr:`stdin` and :attr:`stderr` are not updated by the |
| 422 | :meth:`communicate` method. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 423 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 424 | If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is |
| 425 | passed to the underlying ``CreateProcess`` function. |
Brian Curtin | 3040193 | 2011-04-29 22:20:57 -0500 | [diff] [blame] | 426 | *creationflags*, if given, can be :data:`CREATE_NEW_CONSOLE` or |
| 427 | :data:`CREATE_NEW_PROCESS_GROUP`. (Windows only) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 428 | |
Gregory P. Smith | c9557af | 2011-05-11 22:18:23 -0700 | [diff] [blame] | 429 | Popen objects are supported as context managers via the :keyword:`with` statement: |
| 430 | on exit, standard file descriptors are closed, and the process is waited for. |
Brian Curtin | 79cdb66 | 2010-12-03 02:46:02 +0000 | [diff] [blame] | 431 | :: |
| 432 | |
| 433 | with Popen(["ifconfig"], stdout=PIPE) as proc: |
| 434 | log.write(proc.stdout.read()) |
| 435 | |
| 436 | .. versionchanged:: 3.2 |
| 437 | Added context manager support. |
| 438 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 439 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 440 | Exceptions |
| 441 | ^^^^^^^^^^ |
| 442 | |
| 443 | Exceptions raised in the child process, before the new program has started to |
| 444 | execute, will be re-raised in the parent. Additionally, the exception object |
| 445 | will have one extra attribute called :attr:`child_traceback`, which is a string |
Georg Brandl | 8167561 | 2010-08-26 14:30:56 +0000 | [diff] [blame] | 446 | containing traceback information from the child's point of view. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 447 | |
| 448 | The most common exception raised is :exc:`OSError`. This occurs, for example, |
| 449 | when trying to execute a non-existent file. Applications should prepare for |
| 450 | :exc:`OSError` exceptions. |
| 451 | |
| 452 | A :exc:`ValueError` will be raised if :class:`Popen` is called with invalid |
| 453 | arguments. |
| 454 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 455 | :func:`check_call` and :func:`check_output` will raise |
| 456 | :exc:`CalledProcessError` if the called process returns a non-zero return |
| 457 | code. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 458 | |
| 459 | |
| 460 | Security |
| 461 | ^^^^^^^^ |
| 462 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 463 | Unlike some other popen functions, this implementation will never call a |
| 464 | system shell implicitly. This means that all characters, including shell |
| 465 | metacharacters, can safely be passed to child processes. Obviously, if the |
| 466 | shell is invoked explicitly, then it is the application's responsibility to |
| 467 | ensure that all whitespace and metacharacters are quoted appropriately. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 468 | |
| 469 | |
| 470 | Popen Objects |
| 471 | ------------- |
| 472 | |
| 473 | Instances of the :class:`Popen` class have the following methods: |
| 474 | |
| 475 | |
| 476 | .. method:: Popen.poll() |
| 477 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 478 | Check if child process has terminated. Set and return :attr:`returncode` |
| 479 | attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 480 | |
| 481 | |
| 482 | .. method:: Popen.wait() |
| 483 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 484 | Wait for child process to terminate. Set and return :attr:`returncode` |
| 485 | attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 486 | |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 487 | .. warning:: |
| 488 | |
Philip Jenvey | b089684 | 2009-12-03 02:29:36 +0000 | [diff] [blame] | 489 | This will deadlock when using ``stdout=PIPE`` and/or |
| 490 | ``stderr=PIPE`` and the child process generates enough output to |
| 491 | a pipe such that it blocks waiting for the OS pipe buffer to |
| 492 | accept more data. Use :meth:`communicate` to avoid that. |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 493 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 494 | |
| 495 | .. method:: Popen.communicate(input=None) |
| 496 | |
| 497 | Interact with process: Send data to stdin. Read data from stdout and stderr, |
| 498 | until end-of-file is reached. Wait for process to terminate. The optional |
Georg Brandl | e11787a | 2008-07-01 19:10:52 +0000 | [diff] [blame] | 499 | *input* argument should be a byte string to be sent to the child process, or |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 500 | ``None``, if no data should be sent to the child. |
| 501 | |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 502 | :meth:`communicate` returns a tuple ``(stdoutdata, stderrdata)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 503 | |
Guido van Rossum | 0d3fb8a | 2007-11-26 23:23:18 +0000 | [diff] [blame] | 504 | Note that if you want to send data to the process's stdin, you need to create |
| 505 | the Popen object with ``stdin=PIPE``. Similarly, to get anything other than |
| 506 | ``None`` in the result tuple, you need to give ``stdout=PIPE`` and/or |
| 507 | ``stderr=PIPE`` too. |
| 508 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 509 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 510 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 511 | The data read is buffered in memory, so do not use this method if the data |
| 512 | size is large or unlimited. |
| 513 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 514 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 515 | .. method:: Popen.send_signal(signal) |
| 516 | |
| 517 | Sends the signal *signal* to the child. |
| 518 | |
| 519 | .. note:: |
| 520 | |
Brian Curtin | eb24d74 | 2010-04-12 17:16:38 +0000 | [diff] [blame] | 521 | On Windows, SIGTERM is an alias for :meth:`terminate`. CTRL_C_EVENT and |
Senthil Kumaran | 916bd38 | 2010-10-15 12:55:19 +0000 | [diff] [blame] | 522 | CTRL_BREAK_EVENT can be sent to processes started with a *creationflags* |
Brian Curtin | eb24d74 | 2010-04-12 17:16:38 +0000 | [diff] [blame] | 523 | parameter which includes `CREATE_NEW_PROCESS_GROUP`. |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 524 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 525 | |
| 526 | .. method:: Popen.terminate() |
| 527 | |
| 528 | Stop the child. On Posix OSs the method sends SIGTERM to the |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 529 | child. On Windows the Win32 API function :c:func:`TerminateProcess` is called |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 530 | to stop the child. |
| 531 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 532 | |
| 533 | .. method:: Popen.kill() |
| 534 | |
| 535 | Kills the child. On Posix OSs the function sends SIGKILL to the child. |
| 536 | On Windows :meth:`kill` is an alias for :meth:`terminate`. |
| 537 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 538 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 539 | The following attributes are also available: |
| 540 | |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 541 | .. warning:: |
| 542 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 543 | Use :meth:`communicate` rather than :attr:`.stdin.write <stdin>`, |
| 544 | :attr:`.stdout.read <stdout>` or :attr:`.stderr.read <stderr>` to avoid |
| 545 | deadlocks due to any of the other OS pipe buffers filling up and blocking the |
| 546 | child process. |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 547 | |
| 548 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 549 | .. attribute:: Popen.stdin |
| 550 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 551 | If the *stdin* argument was :data:`PIPE`, this attribute is a :term:`file |
| 552 | object` that provides input to the child process. Otherwise, it is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 553 | |
| 554 | |
| 555 | .. attribute:: Popen.stdout |
| 556 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 557 | If the *stdout* argument was :data:`PIPE`, this attribute is a :term:`file |
| 558 | object` that provides output from the child process. Otherwise, it is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 559 | |
| 560 | |
| 561 | .. attribute:: Popen.stderr |
| 562 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 563 | If the *stderr* argument was :data:`PIPE`, this attribute is a :term:`file |
| 564 | object` that provides error output from the child process. Otherwise, it is |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 565 | ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 566 | |
| 567 | |
| 568 | .. attribute:: Popen.pid |
| 569 | |
| 570 | The process ID of the child process. |
| 571 | |
Georg Brandl | 58bfdca | 2010-03-21 09:50:49 +0000 | [diff] [blame] | 572 | Note that if you set the *shell* argument to ``True``, this is the process ID |
| 573 | of the spawned shell. |
| 574 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 575 | |
| 576 | .. attribute:: Popen.returncode |
| 577 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 578 | The child return code, set by :meth:`poll` and :meth:`wait` (and indirectly |
| 579 | by :meth:`communicate`). A ``None`` value indicates that the process |
| 580 | hasn't terminated yet. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 581 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 582 | A negative value ``-N`` indicates that the child was terminated by signal |
| 583 | ``N`` (Unix only). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 584 | |
| 585 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 586 | Windows Popen Helpers |
| 587 | --------------------- |
| 588 | |
| 589 | The :class:`STARTUPINFO` class and following constants are only available |
| 590 | on Windows. |
| 591 | |
| 592 | .. class:: STARTUPINFO() |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 593 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 594 | Partial support of the Windows |
| 595 | `STARTUPINFO <http://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx>`__ |
| 596 | structure is used for :class:`Popen` creation. |
| 597 | |
| 598 | .. attribute:: dwFlags |
| 599 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 600 | A bit field that determines whether certain :class:`STARTUPINFO` |
| 601 | attributes are used when the process creates a window. :: |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 602 | |
| 603 | si = subprocess.STARTUPINFO() |
| 604 | si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW |
| 605 | |
| 606 | .. attribute:: hStdInput |
| 607 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 608 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 609 | is the standard input handle for the process. If |
| 610 | :data:`STARTF_USESTDHANDLES` is not specified, the default for standard |
| 611 | input is the keyboard buffer. |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 612 | |
| 613 | .. attribute:: hStdOutput |
| 614 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 615 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 616 | is the standard output handle for the process. Otherwise, this attribute |
| 617 | is ignored and the default for standard output is the console window's |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 618 | buffer. |
| 619 | |
| 620 | .. attribute:: hStdError |
| 621 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 622 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 623 | is the standard error handle for the process. Otherwise, this attribute is |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 624 | ignored and the default for standard error is the console window's buffer. |
| 625 | |
| 626 | .. attribute:: wShowWindow |
| 627 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 628 | If :attr:`dwFlags` specifies :data:`STARTF_USESHOWWINDOW`, this attribute |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 629 | can be any of the values that can be specified in the ``nCmdShow`` |
| 630 | parameter for the |
| 631 | `ShowWindow <http://msdn.microsoft.com/en-us/library/ms633548(v=vs.85).aspx>`__ |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 632 | function, except for ``SW_SHOWDEFAULT``. Otherwise, this attribute is |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 633 | ignored. |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 634 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 635 | :data:`SW_HIDE` is provided for this attribute. It is used when |
| 636 | :class:`Popen` is called with ``shell=True``. |
| 637 | |
| 638 | |
| 639 | Constants |
| 640 | ^^^^^^^^^ |
| 641 | |
| 642 | The :mod:`subprocess` module exposes the following constants. |
| 643 | |
| 644 | .. data:: STD_INPUT_HANDLE |
| 645 | |
| 646 | The standard input device. Initially, this is the console input buffer, |
| 647 | ``CONIN$``. |
| 648 | |
| 649 | .. data:: STD_OUTPUT_HANDLE |
| 650 | |
| 651 | The standard output device. Initially, this is the active console screen |
| 652 | buffer, ``CONOUT$``. |
| 653 | |
| 654 | .. data:: STD_ERROR_HANDLE |
| 655 | |
| 656 | The standard error device. Initially, this is the active console screen |
| 657 | buffer, ``CONOUT$``. |
| 658 | |
| 659 | .. data:: SW_HIDE |
| 660 | |
| 661 | Hides the window. Another window will be activated. |
| 662 | |
| 663 | .. data:: STARTF_USESTDHANDLES |
| 664 | |
| 665 | Specifies that the :attr:`STARTUPINFO.hStdInput`, |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 666 | :attr:`STARTUPINFO.hStdOutput`, and :attr:`STARTUPINFO.hStdError` attributes |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 667 | contain additional information. |
| 668 | |
| 669 | .. data:: STARTF_USESHOWWINDOW |
| 670 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 671 | Specifies that the :attr:`STARTUPINFO.wShowWindow` attribute contains |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 672 | additional information. |
| 673 | |
| 674 | .. data:: CREATE_NEW_CONSOLE |
| 675 | |
| 676 | The new process has a new console, instead of inheriting its parent's |
| 677 | console (the default). |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 678 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 679 | This flag is always set when :class:`Popen` is created with ``shell=True``. |
| 680 | |
Brian Curtin | 3040193 | 2011-04-29 22:20:57 -0500 | [diff] [blame] | 681 | .. data:: CREATE_NEW_PROCESS_GROUP |
| 682 | |
| 683 | A :class:`Popen` ``creationflags`` parameter to specify that a new process |
| 684 | group will be created. This flag is necessary for using :func:`os.kill` |
| 685 | on the subprocess. |
| 686 | |
| 687 | This flag is ignored if :data:`CREATE_NEW_CONSOLE` is specified. |
| 688 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 689 | |
Benjamin Peterson | dcf97b9 | 2008-07-02 17:30:14 +0000 | [diff] [blame] | 690 | .. _subprocess-replacements: |
| 691 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 692 | Replacing Older Functions with the subprocess Module |
| 693 | ---------------------------------------------------- |
| 694 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 695 | In this section, "a becomes b" means that b can be used as a replacement for a. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 696 | |
| 697 | .. note:: |
| 698 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 699 | All "a" functions in this section fail (more or less) silently if the |
| 700 | executed program cannot be found; the "b" replacements raise :exc:`OSError` |
| 701 | instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 702 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 703 | In addition, the replacements using :func:`check_output` will fail with a |
| 704 | :exc:`CalledProcessError` if the requested operation produces a non-zero |
| 705 | return code. The output is still available as the ``output`` attribute of |
| 706 | the raised exception. |
| 707 | |
| 708 | In the following examples, we assume that the relevant functions have already |
| 709 | been imported from the subprocess module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 710 | |
| 711 | |
| 712 | Replacing /bin/sh shell backquote |
| 713 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 714 | |
| 715 | :: |
| 716 | |
| 717 | output=`mycmd myarg` |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 718 | # becomes |
| 719 | output = check_output(["mycmd", "myarg"]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 720 | |
| 721 | |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 722 | Replacing shell pipeline |
| 723 | ^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 724 | |
| 725 | :: |
| 726 | |
| 727 | output=`dmesg | grep hda` |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 728 | # becomes |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 729 | p1 = Popen(["dmesg"], stdout=PIPE) |
| 730 | p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE) |
Gregory P. Smith | e09d2f1 | 2011-02-05 21:47:25 +0000 | [diff] [blame] | 731 | p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 732 | output = p2.communicate()[0] |
| 733 | |
Gregory P. Smith | e09d2f1 | 2011-02-05 21:47:25 +0000 | [diff] [blame] | 734 | The p1.stdout.close() call after starting the p2 is important in order for p1 |
| 735 | to receive a SIGPIPE if p2 exits before p1. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 736 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 737 | Alternatively, for trusted input, the shell's own pipeline support may still |
R David Murray | 28b8b94 | 2012-04-03 08:46:48 -0400 | [diff] [blame^] | 738 | be used directly:: |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 739 | |
| 740 | output=`dmesg | grep hda` |
| 741 | # becomes |
| 742 | output=check_output("dmesg | grep hda", shell=True) |
| 743 | |
| 744 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 745 | Replacing :func:`os.system` |
| 746 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 747 | |
| 748 | :: |
| 749 | |
| 750 | sts = os.system("mycmd" + " myarg") |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 751 | # becomes |
| 752 | sts = call("mycmd" + " myarg", shell=True) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 753 | |
| 754 | Notes: |
| 755 | |
| 756 | * Calling the program through the shell is usually not required. |
| 757 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 758 | A more realistic example would look like this:: |
| 759 | |
| 760 | try: |
| 761 | retcode = call("mycmd" + " myarg", shell=True) |
| 762 | if retcode < 0: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 763 | print("Child was terminated by signal", -retcode, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 764 | else: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 765 | print("Child returned", retcode, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 766 | except OSError as e: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 767 | print("Execution failed:", e, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 768 | |
| 769 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 770 | Replacing the :func:`os.spawn <os.spawnl>` family |
| 771 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 772 | |
| 773 | P_NOWAIT example:: |
| 774 | |
| 775 | pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg") |
| 776 | ==> |
| 777 | pid = Popen(["/bin/mycmd", "myarg"]).pid |
| 778 | |
| 779 | P_WAIT example:: |
| 780 | |
| 781 | retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg") |
| 782 | ==> |
| 783 | retcode = call(["/bin/mycmd", "myarg"]) |
| 784 | |
| 785 | Vector example:: |
| 786 | |
| 787 | os.spawnvp(os.P_NOWAIT, path, args) |
| 788 | ==> |
| 789 | Popen([path] + args[1:]) |
| 790 | |
| 791 | Environment example:: |
| 792 | |
| 793 | os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env) |
| 794 | ==> |
| 795 | Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"}) |
| 796 | |
| 797 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 798 | |
| 799 | Replacing :func:`os.popen`, :func:`os.popen2`, :func:`os.popen3` |
| 800 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 801 | |
| 802 | :: |
| 803 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 804 | (child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 805 | ==> |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 806 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 807 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 808 | (child_stdin, child_stdout) = (p.stdin, p.stdout) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 809 | |
| 810 | :: |
| 811 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 812 | (child_stdin, |
| 813 | child_stdout, |
| 814 | child_stderr) = os.popen3(cmd, mode, bufsize) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 815 | ==> |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 816 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 817 | stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True) |
| 818 | (child_stdin, |
| 819 | child_stdout, |
| 820 | child_stderr) = (p.stdin, p.stdout, p.stderr) |
| 821 | |
| 822 | :: |
| 823 | |
| 824 | (child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize) |
| 825 | ==> |
| 826 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 827 | stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True) |
| 828 | (child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout) |
| 829 | |
| 830 | Return code handling translates as follows:: |
| 831 | |
| 832 | pipe = os.popen(cmd, 'w') |
| 833 | ... |
| 834 | rc = pipe.close() |
Stefan Krah | fc9e08d | 2010-07-14 10:16:11 +0000 | [diff] [blame] | 835 | if rc is not None and rc >> 8: |
Ezio Melotti | 985e24d | 2009-09-13 07:54:02 +0000 | [diff] [blame] | 836 | print("There were some errors") |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 837 | ==> |
| 838 | process = Popen(cmd, 'w', stdin=PIPE) |
| 839 | ... |
| 840 | process.stdin.close() |
| 841 | if process.wait() != 0: |
Ezio Melotti | 985e24d | 2009-09-13 07:54:02 +0000 | [diff] [blame] | 842 | print("There were some errors") |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 843 | |
| 844 | |
| 845 | Replacing functions from the :mod:`popen2` module |
| 846 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 847 | |
| 848 | .. note:: |
| 849 | |
| 850 | If the cmd argument to popen2 functions is a string, the command is executed |
| 851 | through /bin/sh. If it is a list, the command is directly executed. |
| 852 | |
| 853 | :: |
| 854 | |
| 855 | (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode) |
| 856 | ==> |
| 857 | p = Popen(["somestring"], shell=True, bufsize=bufsize, |
| 858 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 859 | (child_stdout, child_stdin) = (p.stdout, p.stdin) |
| 860 | |
| 861 | :: |
| 862 | |
| 863 | (child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, mode) |
| 864 | ==> |
| 865 | p = Popen(["mycmd", "myarg"], bufsize=bufsize, |
| 866 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 867 | (child_stdout, child_stdin) = (p.stdout, p.stdin) |
| 868 | |
| 869 | :class:`popen2.Popen3` and :class:`popen2.Popen4` basically work as |
| 870 | :class:`subprocess.Popen`, except that: |
| 871 | |
| 872 | * :class:`Popen` raises an exception if the execution fails. |
| 873 | |
| 874 | * the *capturestderr* argument is replaced with the *stderr* argument. |
| 875 | |
| 876 | * ``stdin=PIPE`` and ``stdout=PIPE`` must be specified. |
| 877 | |
| 878 | * popen2 closes all file descriptors by default, but you have to specify |
Gregory P. Smith | f560485 | 2010-12-13 06:45:02 +0000 | [diff] [blame] | 879 | ``close_fds=True`` with :class:`Popen` to guarantee this behavior on |
| 880 | all platforms or past Python versions. |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 881 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 882 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 883 | Legacy Shell Invocation Functions |
Nick Coghlan | 32e4a58 | 2011-11-08 21:50:58 +1000 | [diff] [blame] | 884 | --------------------------------- |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 885 | |
| 886 | This module also provides the following legacy functions from the 2.x |
| 887 | ``commands`` module. These operations implicitly invoke the system shell and |
| 888 | none of the guarantees described above regarding security and exception |
| 889 | handling consistency are valid for these functions. |
| 890 | |
| 891 | .. function:: getstatusoutput(cmd) |
| 892 | |
| 893 | Return ``(status, output)`` of executing *cmd* in a shell. |
| 894 | |
| 895 | Execute the string *cmd* in a shell with :func:`os.popen` and return a 2-tuple |
| 896 | ``(status, output)``. *cmd* is actually run as ``{ cmd ; } 2>&1``, so that the |
| 897 | returned output will contain output or error messages. A trailing newline is |
| 898 | stripped from the output. The exit status for the command can be interpreted |
| 899 | according to the rules for the C function :c:func:`wait`. Example:: |
| 900 | |
| 901 | >>> subprocess.getstatusoutput('ls /bin/ls') |
| 902 | (0, '/bin/ls') |
| 903 | >>> subprocess.getstatusoutput('cat /bin/junk') |
| 904 | (256, 'cat: /bin/junk: No such file or directory') |
| 905 | >>> subprocess.getstatusoutput('/bin/junk') |
| 906 | (256, 'sh: /bin/junk: not found') |
| 907 | |
| 908 | Availability: UNIX. |
| 909 | |
| 910 | |
| 911 | .. function:: getoutput(cmd) |
| 912 | |
| 913 | Return output (stdout and stderr) of executing *cmd* in a shell. |
| 914 | |
| 915 | Like :func:`getstatusoutput`, except the exit status is ignored and the return |
| 916 | value is a string containing the command's output. Example:: |
| 917 | |
| 918 | >>> subprocess.getoutput('ls /bin/ls') |
| 919 | '/bin/ls' |
| 920 | |
| 921 | Availability: UNIX. |
| 922 | |
Nick Coghlan | 32e4a58 | 2011-11-08 21:50:58 +1000 | [diff] [blame] | 923 | |
| 924 | Notes |
| 925 | ----- |
| 926 | |
| 927 | .. _converting-argument-sequence: |
| 928 | |
| 929 | Converting an argument sequence to a string on Windows |
| 930 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 931 | |
| 932 | On Windows, an *args* sequence is converted to a string that can be parsed |
| 933 | using the following rules (which correspond to the rules used by the MS C |
| 934 | runtime): |
| 935 | |
| 936 | 1. Arguments are delimited by white space, which is either a |
| 937 | space or a tab. |
| 938 | |
| 939 | 2. A string surrounded by double quotation marks is |
| 940 | interpreted as a single argument, regardless of white space |
| 941 | contained within. A quoted string can be embedded in an |
| 942 | argument. |
| 943 | |
| 944 | 3. A double quotation mark preceded by a backslash is |
| 945 | interpreted as a literal double quotation mark. |
| 946 | |
| 947 | 4. Backslashes are interpreted literally, unless they |
| 948 | immediately precede a double quotation mark. |
| 949 | |
| 950 | 5. If backslashes immediately precede a double quotation mark, |
| 951 | every pair of backslashes is interpreted as a literal |
| 952 | backslash. If the number of backslashes is odd, the last |
| 953 | backslash escapes the next double quotation mark as |
| 954 | described in rule 3. |